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I have a problem with my heating system inside the car which is linked to the cooling system somehow. I have a 2002 A4 1.9TDi, when I drive the car at low rev's or sit idling I get heat inside the car, when I start driving at normal 60mph, intermittently I lose hot air inside. I also notice the engine temperature gauge rises when the hot air turns cold and vice versa (climate control set on Hi) although only when driving not sitting stationary.
I have had the water pump changed and the thermostat which has not helped.
I completely flushed (and reverse flushed) through the entire system 2 days ago from the top and the bottom of the radiator and through the heater matrix but it still does the same problem. There did not seem to be any restrictions when flushing.
Additionally, there is no signs of oil in the coolant or water/ coolant in the oil.

Oh, also, after driving, the temperature of the top radiator hose is boiling hot whilst the bottom one is cold. Both hoses in and out of the heater matrix/ core are hot. It would seem that for some reason there is an intermittent blockage in the system or there is some sensor in the system that shuts something off. Although not fully knowing everything about the system I'm kind of stumped for now. My mechanic is also stumped after replacing the water pump and thermostat. His next step was going to be replacing the radiator but I didn't want anymore time spent ont he car at my expense. The last bill was quite hefty!!! especially just before christmas

Does anybody have any ideas? I have seen lots of these forums with people with similar problems, although nobody has come up with a definitive answer. If I do get a solution to this, I fully intend going through a lot of these forums and updating them with the solution to my problem.

Please keep me posted if you get an answer to the problem.
I found on another forum the other day that somebody had a fairly similar problem to ours. They disconnected the hoses from the heater matrix at the back of the engine bay where the aluminium pipes go through the firewall and flushed the matrix with boiling water and oxiclear. Following this there problem was fixed. I tried this and unfortunately I'm still getting the problem. The flush went OK so I'm eliminating the heater matrix itself from being the source of the problem.
The peculiar thing was, when I disconnected the hoses, the matrix was dry!! I can only summise from this, that there is a blockage elsewhere in the cooling system that is causing the coolant fluid to boil.
My next phase is to do a similar flush on both the radiator and the engine block. To do the engine block (accorsing to the haynes manual) I'm going to have to remove the thermostat.

No I still haven't managed to get this sorted yet. A couple of weeks back I removed the thermostat and flushed the entire system through the engine block etc. I ran the car with the thermostat out for a few miles and still seemed to get the same problem. Although with the thermostat out the engine runs a lot cooler but you still notice the temperature variations slightly.
I am now going through this over and over in my mind to try and get to the bottom of this. I remember reading on another post/ forum about another guy who was having similar problems. He changed his radiator out and that seemed to fix it. All I can summise from this is that there is a restriction in the radiator that when a high flow rate tries to pass through, it creates a sufficiently high back pressure almost restricting the flow enough to allow the fluid to boil and therefore vent off.
I'm not going to have time in the next few weeks to try a new radiator, so I'll just have to run it the way it is and keep topping up the coolant fluid.
If you manage to get an answer to this, please post back. This seems to be a very common problem with no definitive answer to the solution!!!

Hi I've been reading posts to see if anyone is having the same problem I am having. I own a 2001.5 1.8T A4. During the fall I took it in to resolve a heating problem. At that time the heat was not as hot as I expected. Sometimes it was ok, other times it was cool, not cold.
The dealer recommended a rad/heater core flush, which I did. When I got the car back the heat was working, still not HOT but better.
Last week in driving in -8C weather it went cold again and stayed there for a day or so, I called the dealer to try again. Befor I got to the dealer, it was OK again,not great but warm enough to slow the fan to 2 bars. (if you have one you know what I mean)
The dealer recommended a new heater core. I didn't think that was the problem because it sometimes works.
Questions:
1 Is there a heater control valve and if so, where is this? Have these been known to stick or be intermittent? is there a VAG code if it doesn't work?
2 Where is the motor that controls the damper that mixes hot and cold air? Again could this be the problem. Is there a code for this.

The dealer does not believe these are theproblems, but cannot explain why the problem is intermittent.
BTW, the dealer implied that another flush "might" help because, since the coolent does not get changed on a regular basis, sludge builds up and can cause heater plugging. Is this like to oil sludge problem????
Thanks for any help or advice.
Barry

hi i have flushed out the whole system in my 1.9 tdi and the heat is a little better,but still not as hot as it should be.you can run the fan on the second bar and you have a little head but not much.would it be possible for the heat control panel to send a wrong signal and not allowing the flaps in the heater box not to open enough to let the heat out??:.help please

just a bit of an update,i borrowed a climate control box from my brother in laws a4 to see if it helped and it was no different so i can rule that out.i have stripped half the dash out to check that all my flaps wer working in the heater box and they all seem fine to me.i took the cover off my heater matrix and have found that the bottom pipe going into it was very hot and the top one was almost cold so i think this may be my problem. i im gong to buy a new one and try it.i tried to wash the old one but it must be clogged solid with gunge.i will letu now the results,good i hope